This invention relates to a fluorescent lamp and, more particularly, to a fluorscent lamp in which reduction of the mechanical strength of the bulb and reduction of the luminous efficiency due to interaction of phosphor and glass constituting the bulb are prevented.
The fluorescent lamp is generally manufactured by coating fluorescent particles in the form of a film on the inner surface of the bulb, evacuating the bulb through an exhaust tube, activating the electrode material, filling mercury and starting gas in the bulb, and tipping the exhaust tube. When manufacturing a fluorescent lamp of a curved or bent tube, a step of curving or bending the tube is additionally provided.
In the process of manufacture of the florescent lamp as described above, the bulb is heated several times. Since the phosphor particles are in direct contact with the bulb, it is likely that phosphor particles will sink into the softened inner surface or a component of the phosphor will be dissolved or dispersed in the glass constituting the bulb, thus reducing the mechanical strength of the bulb. Therefore, the bulb is readily broken or damaged by an external shock. Further, in some cases it is likely that a glass component intrudes into the phosphor film to reduce the luminous efficiency of the fluorescent lamp. These phenomena are extremely remarkable in the case where lead-activated barium silicate phosphor (BaSi.sub.2 O.sub.5 :Pb), which has a chemical structure resembling glass, is employed.